Depending on whom you ask, the definition for disaster recovery can range from restoring data from a backup to restarting operations at an alternative business continuance site. This chapter will use the Wikipedia definition, which defines disaster recovery as "The ability of an infrastructure to restart operations after a disaster."
The first is how you know when you've successfully recovered from the disaster. There are two common metrics for recovery:
- A recovery point objective (RPO) specifies the point in time at which your capabilities will return when recovery is complete. Let's say you do a daily full backup at 2 a.m. If you have a failure Tuesday at 8 a.m., your RPO will probably be 2 a.m. Tuesday; in other words, your recovery will succeed if you can recover the state of your Exchange data to that particular point in time.
- A recovery time objective (RTO) specifies the maximum amount of time allowed for a recovery. For example, if your service level agreement (SLA) promises that you'll restore operations within six hours of a disaster, you have a six-hour RTO.
Although these metrics are clearly related, there are significant differences between them that become apparent as you start to consider how to reduce the RTO or move the RPO closer to the actual beginning of the outage. To shorten the interval between a failure and your RPO, you must make more frequent copies of your data with whatever protection mechanism you've chosen. To shorten the RTO, you need to take measures to increase the speed of your recovery. The remainder of this chapter will discuss both types of measures.
10 tips in 10 minutes: Fundamentals of Exchange Server disaster recovery
Tip 1: Defining Exchange disaster recovery
Tip 2: How Exchange backs up data
Tip 3: Choosing a backup type for Exchange
Tip 4: Online vs. offline Exchange Server backups
Tip 5: Basic Exchange backup and restore
Tip 6: Exchange vendor snapshots and point-in-time copies
Tip 7: VSS for Exchange
Tip 8: Exchange Server replication
Tip 9: Exchange design choices and issues
Tip 10: Exchange disaster recovery planning
This chapter excerpt from the free e-book The Definitive Guide to Exchange Disaster Recovery and Availability, by Paul Robichaux, is printed with permission from Realtimepublishers, Copyright 2005. Click here for the chapter download or download all available chapters here.